1. Field of the Invention
The present invention relates to an X-ray detector and, more particularly, to an X-ray detector panel including a thin film transistor (TFT) and a PIN diode.
2. Description of the Related Art
An amount of X-rays, which have wavelengths ranging between those of visible rays and gamma rays, and which may be transmitted through solids, varies according to the densities of the solids. An inside of an object may be imaged by measuring the amount of X-rays transmitted through the object.
Photosensitive films were used for a long time to record X-ray images. However, in X-ray digital radiography (DR), which is recently advancing, X-ray detectors are used to acquire X-ray images.
X-ray detectors may be roughly categorized into either a charge coupled device (CCD) type or a flat panel (FP) type. However, these types are both based on a basic principle in which charges photoelectrically generated in units of pixels are converted into digital signals by an analog-to-digital converter (ADC). However, CCD X-ray detectors may have low efficiency and resolution since CCDs may be not large enough to receive the entire incident light.
FP X-ray detectors may be further divided into a direct type and an indirect type. Direct FP X-ray detectors directly convert quanta of X-rays into charges. Indirect FP X-ray detectors convert X-rays into visible rays first, and then convert the visible rays into charges. In both direct and indirect FP X-ray directors, the charges converted from X-rays or visible rays are transferred to an amplifier and an analog-to-digital converter (ADC) via a thin film transistor (TFT) switching device. Direct FP X-ray detectors do not require additional steps, but are disadvantageous in terms of low X-ray conversion efficiency, high-voltage requirement, short lifespan of a semiconductor layer for converting X-rays into charges, and the like. For these reasons, indirect FP X-ray directors are currently widely used.
An indirect FP X-ray detector includes a scintillator layer and a flat panel under the scintillator layer. The flat panel is an array of pixels, each pixel including a PIN diode and a TFT. In particular, according to the operating principle of direct FP X-ray detectors, X-rays emitted from an X-ray source are transmitted through an object, and are then converted into visible rays in the scintillator layer. The visible rays are then incident onto the PIN diodes of the flat panel so that electrons are generated in the PIN diodes and are read by the TFTs. Signals read from each pixel in such a manner are digitized by an ADC, and are finally realized as digital images on a monitor.